Safer potential Zika vaccine discovered

Researchers have identified a potential vaccine that may defend against Zika virus without producing antibodies.

Many reports show that antibodies against Zika virus can worsen dengue virus infection, which, like Zika, is caused by a mosquito-borne virus, said researchers from the University of Nebraska-Lincoln in the US.

This phenomenon is referred to as antibody-dependent enhancement (ADE) of disease.

This has been an obstacle to the development of effective and safe dengue virus vaccines.

"If you have immunity to one of these viruses and get infected by a second one, the illness can be much worse," said Eric Weaver from the University of Nebraska-Lincoln.

"The body makes the wrong immune response," Weaver said.

First discovered in Uganda's Zika Forest in 1947, the virus initially was believed to cause only mild or asymptomatic infection in humans.

However, outbreaks in Brazil in 2015 and 2016 resulted in higher than historical rates of congenital birth defects in babies born to infected mothers and an increase in the neurological disorder Guillain-Barre syndrome in adults.

In 2016, between 500,000 to 1.5 million suspected cases of Zika infection were reported worldwide, with 4,300 related cases of microcephaly, or abnormally small heads, in infants, researchers said.

Doctoral student Brianna Bullard developed a genetically altered version of Adenovirus while working with Weaver as an undergraduate.

In a study published in the journal Scientific Reports, the scientists used two forms of attenuated Adenovirus to serve as vectors to deliver the Zika vaccine.

Adenoviruses, which typically cause mild illness such as the common cold, are modified so that they are replication-defective and incapable of causing disease.

The modified, or attenuated viruses, are regarded as safe and highly effective vaccine vectors capable of inducing long-lasting protective immune responses against infectious pathogens.

They inserted the prM-E structural genes of Zika into key areas of Adenovirus Type 4 and Adenovirus Type 5 genomes.

Tested in mice, both vaccines offered strong T-cell responses and substantial protection against Zika infection.

However, the vaccine based on Type 4 Adenovirus induced strong T-cell responses with undetectable antibodies.

T cells are a type of white blood cell that are at the core of the system that tailors the body's adaptive immune response to specific pathogens.

"To our knowledge, this is the first report of a vaccine that uses the prM-E genes of Zika virus to induce protective immunity without inducing anti-Zika virus antibodies," Weaver said.

"The lack of antibodies may very well circumvent the potential risks of ADE resulting in an effective and safer vaccine than those currently in clinical trials," he said.